General
The RA system supplies data to the:
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Left, center, and right AFDCs

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TCAS computer

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Left and right weather receiver transmitters

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GPWC

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Left and right AIMS cabinets

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Left, right, and center PFCs (through the AIMS cabinets).

Altitude Data
Radio altitude goes to the AIMS for PFD displays and status messages.
Each AFDC gets radio altitude from its onside RA transceiver. The AFDCs use radio altitude in their approach control calculations.
The GPWC uses radio altitude in its ground proximity alert and warning logic calculations.
The TCAS computer uses radio altitude to set the sensitivity levels and for intruder advisory calculations.
Weather radar (WXR) uses radio altitude data for the following:
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Automatic on/off logic

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Alert and display logic.

Fault Summary Data
Fault data from each radio altimeter goes to the AIMS cabinets. The AIMS cabinets send data to the status page. The status page shows RA status messages.
The CMCF of the AIMS cabinets receives and stores RA fault information. Maintenance personnel use the MAT to get fault information.
Radio Minimums GPWC Interface
Radio minimums and radio altitude go to the GPWC for various modes of warning.
Radio Minimums Interface
The EFIS control panels supply radio minimums values to the AIMS. The control display units (CDUs) supply backup radio minimums values to the AIMS.
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RA SYSTEM -DATA BUS OUTPUTS, RADIO MINIMUMS INTERFACE

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RA SYSTEM -CMCF INTERFACE

CMCF Interface
The central maintenance computing function (CMCF) of the airplane information management system (AIMS) does tests and monitors the status of the RA system. Maintenance technicians use the maintenance access terminal (MAT) to interface with the CMCF.
The MAT data goes to the AIMS cabinets. The left AIMS cabinet sends the data to the RA system to start a test. If the left AIMS cabinet fails, data goes from the right AIMS cabinet to the RA system through the left AIMS cabinet.
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777 AIRCRAFT MAINTENANCE MANUAL

RA SYSTEM -CMCF INTERFACE

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RA SYSTEM -RA TRANSCEIVER

Purpose
The RA transceiver calculates radio altitude.
The RA transceiver has a non-volatile memory which stores fault information from the last sixty-three flights. It can store up to thirteen faults per flight. Only shop personnel read the non-volatile memory information.
Operational Characteristics
These are the operational characteristics of the transceiver:
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Frequency = 4235 MHz to 4365 MHz

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Transmit power = 500 mw nominal

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Operating range = -20 to 2500 feet.

A test connector on the front panel connects test equipment for shop tests.
Operation
These are the three LED status indicators on the front panel:
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A red or green LRU STATUS LED shows the transceiver operational status. It comes on green when the transceiver is OK. It comes on red when the transceiver has a fault

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A red XMIT ANT FAIL LED shows a transmission antenna or coax cable fault

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A red REC ANT FAIL LED shows a receive antenna or coax cable fault.

You push the test switch to start a self-test.
Training Information Point
The maintenance manual and the fault isolation manual do not have a task for the line maintenance technician to do a test from the front panel of the RA transceiver. You must do all tests for the RA transceiver from the MAT or a PMAT.
Many LRUs on the 777 are compatible with other model airplanes that do not have a central maintenance computing system (CMCS). For that reason these LRUs have a front panel test feature.
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777 AIRCRAFT MAINTENANCE MANUAL

RA SYSTEM -RA TRANSCEIVER

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RA SYSTEM -RA ANTENNA

Purpose
The RA system uses six antennas that transmit and receive RF signals. Each RA xcvr has a transmit and receive antenna. The transmit and receive antenna are the same and interchangeable.
Physical Description
Four screws attach each antenna to the bottom of the fuselage. There is an O-ring seal in a groove around the electrical connector. The O-ring seal supplies moisture protection. The radiation side of the antenna has red markings "FWD" and "DO NOT PAINT".
　
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